Method of manufacturing a magnetic recorder head

ABSTRACT

A method of manufacturing a magnetic recorder head in which a glass frit layer is applied and preliminarily bonded to the front surfaces of a pair of ferromagnetic pieces forming the head, after which the pieces are pressed together at a predetermined pressure and at a temperature exceeding the softening temperature of the glass until an effective gap of a desired width is formed. An article manufactured according to this method.

flnited States Patent Sommer Oct. 23, 1973 [54] METHOD OF MANUFACTURING A 3,529,349 9/1970 Van De Schoot 65/43 MAGNETIC RECORDER HEAD 3,222,150 12/1965 Shepard 65/32 [76] Inventor: Alfred Sommer, 257 Elm Ave.,

Teaneck, NJ. 07666 Primary ExaminerAlfred L. Leavitt Assistant Examiner-Frank Frisenda, Jr.

[22] Flled' 1971 Attorney-Joseph M. Lane et al. [21] Appl. No.: 211,472

Related US. Application Data Continuation of Ser. No. 9,795, Feb. 9, 1970, abandoned.

US. Cl 156/89 65/36, 65/43,

65/59, 156/155 Int. Cl. C03c 27/02 Field of Search t. 156/89, 155, 320; 65/59, 36, 32,43, 18; 79/1002; 29/603, 472.1

References Cited UNITED STATES PATENTS 2/1970 Varadi et al. 156/230 [57] ABSTRACT A qd Lia lfasu rjn ama net c recorderiwadr 2 Claims, 6 Drawing Figures HUI! PAIENIEllum 23 ms ulnu METHOD OF MANUFACTURING A MAGNETIC RECORDER HEAD CROSS REFERENCE TO RELATED APPLICATION This application is a continuation of application Ser. No. 9,795, filed Feb. 9, 1970, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a method of manufacturing a magnetic recorder head, and more particularly, to such a method utilizing a glass bonding between two magnetic pieces to form the head.

Various methods have been proposed to manufacture magnetic recording heads. According to some proposals, a shim, or the like, is placed between two magnetic pieces to mechanically set the final gapthickness. However, the manufacturing difficulties encountered in handling all these pieces are substantial. Also, since the two magnetic pieces must be subsequently joined together in a separate step, the method is time consuming and, therefore, expensive.

Other techniques employ the use of transfer tape, or the like, to adhesively bond a glass layer to one or more of the magnetic pieces, followed by a heating and pressing of the assembly to establish the final gap width. However, these methods suffer from the fact that it is difficult, if not impossible, to control and/or'check the assembly during the manufacturing steps. As a costly result, any defects in the assembly cannot be detected until the product is completed, orat least until it is in its final stages of manufacture.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a method of manufacturing a magnetic recorder head in which a glass layer is utilized both to de- Toward the fulfillment of this object, the method of the present invention comprises the step of applying a glass frit layer to at least one of the front surfaces of the magnetic pieces, preliminarily bonding the glass to said surface to establish a preliminary gap width, and then pressing said pieces together at a predetermined pressure and at a temperature exceeding the softening temperature of said glass until the final gap width is achieved.

Brief Description of the Drawings the manufacture of the recording heads of the present invention;

FIG. 2 is an enlarged perspective view of an individual block cut from the bar of FIG. 1 which has been ground into an elongated head core;

FIG. 3 is an enlarged partial cross-sectional view of the transfer tape utilized in the present invention;

FIG. 4 is a view similar to FIG. 2, but showing the front surfaces of the elongated head core of FIG. 2 treated with a glass layer;

FIG. 5 is a perspective view of an assembled pair of matching elongated head cores; and

FIG. 6 is a perspective view of an individual head core that has been bonded and sliced from the assembled head core of FIG. 5.

Description of the Preferred Embodiments Referring specifically to FIG. 1 of the drawings, the reference numeral 10 refers, in general, to a stock bar which is formed of a ferromagnetic material, and which is adapted to be cut up into a plurality of individual blocks 12. According to the present invention, each in dividual block 12 is form ground into an elongated head core shown generally in FIG. 2, and having a generally U-shaped cross section consisting of a base 14 and a pair of arm portions 16 and 18. The arm portion 16 is tapered slightly so that its front surface 20 is slightly smaller in height than the front surface 22 of the arm 18.

After the form grinding, the surfaces 20 and 22 are lapped or polished to a very high degree to assure that they are flat, and to reduce or eliminate surface irregularities.

A pair of glass frit layers are applied to the front surfaces 20 and 22, respectively, of the block 12 by utilizing a transfer tape 24, which may be of any commercially known variety, such as a type described by the Vitta Corporation in their Bulletin No. G01, dated May I, 1967. The tape is shown in detail in FIG. 3 and consists of a glass frit layer 26 having an adhesive layer 28 coated to one surface thereof, and a plastic sheet 30 extending overthe other surface thereof. A sheet 32 is provided which serves as a backing material for the adhesive layer 28. The glass frit layer is of a thickness greater than the width of the gap that is finally formed and is applied to the surfaces 20 and 22 by removingthe sheet 32 and pressing the tape against each surface so that the adhesive adheres thereto. The plastic sheet 30 is then removed to expose the glass fritlayer 26.

According to a main feature of the present invention, the resulting assembly is then heated to a temperature which exceeds the softening temperature of the glass in order to effect a preliminary bonding of the glass to the surfaces 20 and 22.

The exact temperature required to achieve this preliminary bond can vary as long as it causes the glass to exceed its softening point, or the point at which the glass has a viscosity of 10- poises. It can be appreciated that this temperature will vary in accordance with the particular materials involved, and, in general, should be between 500 and 800F. In any-case,-the

temperature required to achieve the preliminary bond will also be sufficient to burn off the adhesive layer 28 and to effect at least a partial vitrification of the glass.

frit layer 26. The assembly is then allowed to cool and the glass layers formed as a result of the preliminary bond are shown by the reference numerals 34 and 36 on the surfaces 20 and 22, respectively, in FIG. 4, the thickness of each layer being exaggerated for convenience of presentation. The purpose and advantages of the forming of these layers 34 and 36 by the preliminary bonding will be outlined in detail later.

After forming the layers 34 and 36, a matching block 12a, identical in shape to the block 12, is placed in juxtaposition with the block 12 as shown in FIG. 5. The front surfaces of the block 12a may or may not have a glass layer formed thereon in a manner identical to that described above. In the event there is no glass layer formed on the front surfaces of the block 12a, the layers 34 and 36 will be of a thickness to form a pair of effective gaps 38 and 40 of a width which is greater than the effective gap width which is finally formed. Of course, if a glass layer is in fact formed on the front surfaces of the block 12a, these layers, as well as the layers 34 and 36, will be approximately one-half the width of the effective gaps 38 and 40.

The two blocks 12 and 12a arranged in the above manner are then placed between a pair of metal platens, or the like, and inside a furnace wherein they are compressed to a predetermined pressure at a predetermined temperature exceeding the softening temperature of the glass, so that the glass flows outwardly from between the surfaces until the desired final effective gap width is achieved. The assembly is then cooled and the glass remaining in the gaps between the front surfaces of the blocks 12 and 12a bonds the blocks together.

The assembled unit is then sliced in a direction along the dotted lines as shown in FIG. to form a plurality of individual head cores, one of which is shown by the reference numeral 42 in FIG. 5. The glass remaining between each pair of facing surfaces forms a pair of effective gaps 44 and 46 of the desired width, and presents a very smooth surface over which the tape or other recording media travels in a direction indicated by the arrow.

The forming of the glass layers 34 and 36 on the block 12, and possibly on the block 120, provide several distinct and unique advantages. For example, the layers establish a preliminary gap width which enables preliminary tests or checks to be made on the assembly before the final product is formed. One of the most important tests is to check the precise width of the preliminary gap in order to ascertain whether or not it is in a range that will insure that the precise final gap width within predetermined tolerances. Another important test is to determine whether or not the glass is compatible with the ferromagnetic material from an expansion standpoint. In particular, if the type of glass used has a high coefficient of expansion relative to the ferromagnetic material it may strain the latter after the bonding. Therefore, the establishment of the preliminary gap width will enable the ferromagnetic material to be examined for strain.

The above tests may be made either electrically by checking inductive levels, frequency characteristics, permeability, etc., or optically utilizing a high powered microscope, an inframeter, etc.

As an example of the particular steps of the method of the present invention, a block bar of a ferromagnetic material, having dimensions of 6 X 2 X linches, is cut up into a plurality of individual bars having dimensions of 6 X 0.] X 0. linch. Each of these individual bars are ground into an elongated head core shaped as shown in FIG. 2 and having a length of 6 inches, a width of 0.05 inch and a height of 0.1 inch. The transfer tape 24 is applied to both front surfaces and 22 of the core in accordance with the foregoing, and the temperature of the assembly raised to approximately 500F. until the adhesive which adheres the glass layers to the surfaces 20 and 22 is burned off, and the glass is at least partially vitrified and bonded to the front surfaces to form approximately one-half of the preliminary gap widths.

The assembly is then allowed to cool and is checked in accordance with the foregoing. If the checks reveal an acceptable preliminary gap width and the absence of strain on the ferromagnetic member, the block 12 is positioned relative to a matching block 12a as shown in FIG. 5, the blocks are placed between two platens in an electrical oven at a pressure of between 1,000 and 3,000 psi, and the temperature is raised from room temperature to a temperature of approximately 575 in 15-20 minutes. This causes a flowing of a portion of the glass from between the facing surfaces until the platens attain a position whereby the desired effective gap width is achieved, which may be, for example, approximately microinches. The assembly is allowed to cool with the platens maintained at this latter position, and the elongated head core thus formed is sliced into a plurality of individual head cores having a thickness of 0.02 inch.

Thus, as a result of the above method, the advantages of the use of the glass layer are retained, while considerable cost and time savings are achieved as a result of the establishment of the preliminary gap width, as discussed above.

Several variations in the above can be made without departing from the scope of the invention. For example, since the effective gap 46 is normally not utilized in the magnetic recording process, it is not absolutely necessary that a glass material from the gap here. Rather, other means of bonding the front surfaces defining this gap may be utilized, such as a standard epoxy, etc. Of course, the blocks may be initially form ground in a manner that eliminates the effective gap 36 altogether.

I claim:

1. A method of manufacturing a magnetic recorder head having at least one magnetic member and at least one effective gap formed between two adjacent surfaces of said member, said method comprising the steps of adhesively bonding a glass frit layer to one of said surfaces, heating said layer and said one surface to a temperature sufficient to burn off the adhesive and bond said glass to said one surface, allowing the assembly to cool so that said bonded glass establishes a preliminary gap width greater than the first gap width desired, and then pressing said surfaces together with said glass therebetween at a predetermined pressure and temperature exceeding the softening temperature of said glass until said final gap width is achieved.

2. A method of manufacturing a magnetic recorder head having at least one magnetic member and at least one effective gap formed between two adjacent surfaces of said member, said method comprising the steps of adhesively bonding a glass frit layer to both of said surfaces, heating said layer and said surfaces to a temperature sufficient to burn off the adhesive and bond said glass to said surfaces, allowing the assembly to cool so that said bonded glass on each surface establishes a preliminary gap width greater than one half the final gap width desired, and then pressing said surfaces together with said glass therebetween at a predetermined pressure and temperature exceeding the softening temperature of said glass until said final gap width is achieved.

P0405) UNITED STATES PATENT OFFICE cm'rmclmz or CORREC'HON Patent No- 3 6 I Dated ctober 72 I 1Q")? Alfred Sommer Invcntor(s) It is certified that error appears in the above-identified patent said Letters Patent are hereby corrected as shown below:

and that Column 2, line 54, change "800F." to read -800C.,. Column 3 line 46 change high coefficient" to read -low coefficient., Column 3, line 54, change "inframeter" to read -interferometer-. V Column 4, line 30, change "from" to read fo m. Column 3, line 65, 500 1 3,," should read 500 C.

Signed and sealed this 26th day of Ma 19m.

(SEAL) Attes t:

EDWARD MQFLETCHER R. c. MABSHALL- DANN Attesting Officer l V Commissioner of Patents 

1. A method of manufacturing a magnetic recorder head having at least one magnetic member and at least one effective gap formed between two adjacent surfaces of said member, said method comprising the steps of adhesively bonding a glass frit layer to one of said surfaces, heating said layer and said one surface to a temperature sufficient to burn off the adhesive and bond said glass to said one surface, allowing the assembly to cool so that said bonded glass establishes a preliminary gap width greater than the first gap width desired, and then pressing said surfaces together with said glass therebetween at a predetermined pressure and temperature exceeding the softening temperature of said glass until said final gap width is achieved.
 2. A method of manufacturing a magnetic recorder head having at least one magnetic member and at least one effective gap formed between two adjacent surfaces of said member, said method comprising the steps of adhesively bonding a glass frit layer to both of said surfaces, heating said layer and said surfaces to a temperature sufficient to burn off the adhesive and bond said glass to said surfaces, allowing the assembly to cool so that said bonded glass on each surface establishes a preliminary gap width greater than one half the final gap width desired, and then pressing said surfaces together with said glass therebetween at a predetermined pressure and temperature exceeding the softening temperature of said glass until said final gap width is achieved. 